PROJECT SUMMARY/ABSTRACT Parkinson's disease (PD) is a devastating neurodegenerative disorder which has no cure or disease-modifying therapy. One of the greatest obstacles for developing a disease-modifying therapy for PD is the lack of early diagnosis. To date, there is no definite, sensitive and predictive laboratory test available that can identify individuals well before they show clinical manifestations. The availability of early diagnosis of PD would be of utmost importance for the development of a disease-modifying or preventive therapies before the irreversible brain damage has already occurred. The pathological hallmark of PD is the cytoplasmic deposition of amyloid- like aggregates mainly composed of alpha-synuclein (?Syn) termed as Lewy bodies. Compelling evidence suggests that the central event in PD is misfolding and aggregation of ?Syn. The misfolding and aggregation of ?Syn follows a nucleation-dependent mechanism which involves the formation of several intermediate species including soluble ?Syn oligomers and protofibrils. Alpha-synuclein oligomerization is a key event in PD pathogenesis that begins years or decades before the appearance of clinical signs. Most importantly, recent studies have suggested that these ?Syn oligomers circulate in biological fluids such as cerebrospinal fluid (CSF) and blood. Thus, we hypothesize that the detection of these circulating misfolded ?Syn oligomers holds promise for diagnosis of PD and related synucleinopathies. We have recently reported protein misfolding cyclic amplification (PMCA) assay for the detection of misfolded ?Syn oligomers in CSF. Using this PMCA technology, we have been able to differentiate PD patients from control individuals affected by other neurodegenerative (ND) or non-neurodegenerative (NND) disorders with high specificity and sensitivity. The main goal of this application is to expand the applicability of this technology to detect small amounts of ?Syn oligomers present in blood so that a cheap, noninvasive and reliable diagnostic test could be developed. To achieve this goal, we will optimize the assay conditions for sensitive and specific detection of ?Syn oligomers in human blood plasma. Then, we will use well- characterized plasma samples from PD patients, individuals affected with other synucleinopathies, and healthy controls. Next, the sensitivity and specificity of ?Syn-PMCA for PD will be evaluated using a large number of plasma samples from PD patients, age-matched healthy controls, and individuals affected from ND and NND. Finally, we will attempt to correlate the kinetic parameters of ?Syn-PMCA with clinical data at different stages of PD. The findings obtained here will lay the foundation for the development of low cost, non-invasive diagnosis of individuals at risk of developing PD and other synucleinopathies. Our findings will not only help to understand the mechanisms implicated in PD progression but also will provide a window for disease prevention and intervention.